
Ublas : 
Subject: Re: [ublas] fixed size vector in boost::numeric::ublas?
From: David Bellot (david.bellot_at_[hidden])
Date: 20100723 03:25:18
Hi Markus,
sounds a good idea. Let me investigate this. It's in fact on the todo list
so it's very welcome.
Cheers,
David
On Fri, Jul 23, 2010 at 00:16, Markus Grabner <grabner_at_[hidden]> wrote:
>
> Hi all!
>
> In boost::numeric::ublas, there exist different vector variants
> (unbounded and bounded). All of them can be resized dynamically (up to a
> maximum size defined at compile time in the case of the bounded vector).
> Therefore the vector class (or the underlying storage array) have a size
> member which indicates the current size of the vector.
>
> However, it would be extremely useful to have a vector of fixed size, i.e.,
> one which can't be resized dynamically, but has its size statically defined
> at compile time. Such a vector does not require a size member and only
> consumes N*sizeof(T) bytes of storage, where N is the (static) vector size
> and T the value type. Many libraries dealing with geometric data (OpenGL
> and
> OpenInventor being prominent examples) store their data in compact arrays
> in
> their native data types, e.g., the values (x0,y0,z0,x1,y1,z1,x2,y2,z2)
> stored in consecutive memory locations define three points in 3D space. By
> means of a fixed size vector, the entire boost::numeric::ublas
> functionality
> could be applied to such arrays by a simple reinterpret_cast on each
> element. This is not possible with the bounded or unbounded vectors since
> the vector must be constructed before with its size member properly
> initialized, and the actual vector data must therefore be copied explicitly
> before use.
>
> I tried to create a fixed_array class to implement this proposal (see
> attachment), it can be used, e.g., to create the equivalent of the
> OpenInventor "SbVec3f" data type as follows:
>
> typedef boost::numeric::ublas::vector<float,fixed_array<float,3> > vec3d_t;
>
> It is probably not the cleanest solution, and I skipped the serialization
> stuff altogether, but it demonstrates an approach how this can be done.
>
> Is such a feature already available in ublas and did I just miss it? If
> not,
> what do you think about adding it to improve boost's interoperability with
> other libraries?
>
> Thanks & kind regards,
> Markus
>
>
> 
> Markus Grabner
> Institute for Computer Graphics and Vision
> Graz University of Technology, Inffeldgasse 16a/II, 8010 Graz, Austria
> WWW: http://www.icg.tugraz.at/Members/grabner
>
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>
 David Bellot, PhD david.bellot_at_[hidden] http://david.bellot.free.fr